This appl. is a 371 of PCT/EP 99/01956 filed Mar. 20, 1999.
The invention relates to a process for manufacturing an epoxide by reaction between an olefin and a peroxide compound in the presence of a zeolite-based catalyst. The invention relates more particularly to a process for manufacturing 1,2-epoxypropane (or propylene oxide) by reaction between propylene and hydrogen peroxide.
It is known practice to manufacture propylene oxide by epoxidation of propylene using hydrogen peroxide in the presence of a catalyst of the type TS-1, as described, for example, in patent application EP 0,230,949. This known process has the drawback of leading, under certain conditions, to low selectivities.
The invention is directed towards overcoming this drawback by providing a process for manufacturing an epoxide which is of high selectivity.
The invention consequently relates to a continuous process for manufacturing an epoxide, according to which an olefin is reacted, in a reactor in the liquid phase, with a peroxide compound in the presence of a zeolite-based catalyst and in the presence of a solvent, and a gaseous compound is introduced continuously into the reactor at a flow rate which is sufficient to entrain at least some of the epoxide produced, which is recovered with the gaseous compound at the point at which it leaves the reactor.
One of the essential characteristics of the invention lies in the introduction of a gaseous compound into the reactor. The reason for this is that it has been observed that the epoxide reacts in the epoxidation reaction medium with the water and the solvent to form by-products which reduce the selectivity of the epoxidation reaction. It has now been found that by introducing a gaseous compound into the reaction medium at a flow rate which is sufficient to allow the epoxide produced to be entrained and to remove it from the reactor at the same time as the gaseous compound, the contact time between the epoxide produced and the epoxidation reaction medium is reduced. The formation of by-products is thus avoided and the selectivity of the epoxidation is increased.
The function of the gaseous compound is to entrain the epoxide produced out of the reaction medium in order to prevent the epoxide from remaining in contact with the reaction medium for too long, and thus to avoid the formation of by-products. In other words, the gaseous compound allows the epoxide produced to be removed from the reaction medium by stripping.
The gaseous compound used in the process according to the invention can be any compound which is in gaseous form under the epoxidation conditions and which has no negative influence on the epoxidation reaction. It can be chosen from inert gases such as nitrogen.
One advantageous embodiment of the process according to the invention consists in introducing, into the reactor, the olefin in gaseous form and in a large excess such that the gaseous olefin can act, partially or completely, as the gaseous compound, i.e. it can entrain the epoxide produced and remove it from the reactor.
Another specific embodiment of the process according to the invention consists in introducing the gaseous compound into the reactor at a flow rate such that it makes it possible not only to entrain at least some of the epoxide produced, but also to circulate the liquid phase in the reactor, in particular when this reactor is a loop-type reactor.